Secondary blasting unit



April 1966 G. T. WOFFORD m, ETAL 3,244,102

SECONDARY BLASTING UNIT Filed July 9, 1964 m D l ROW T Fm O 5 RA W A O TA O E V E N AM E J L G H W W E G 3 2 2 2 ATTORNEYS United States Patent3,244,102 SECONDARY BLASTING UNIT George Thomas Wofford III, James E.Darrough, and William Don McFerrin, all of 1560 Idlewild Drive, Reno,Nev.

Filed July 9, 1964, Ser. No. 381,439 Claims. (Cl. 10224) The inventionrelates to the movement of rocks, earth comparable material by explosivetechniques and is especially concerned with a device for use after aninitial blast has broken up the terrain for reducing large rocks,boulders and the like into fragments which can be more readily handled.

When an explosive charge is detonated to blow down a rock wall or todislodge comparable materials from their original place, there is a gooddeal of shattering and fragmentation of the material, but in someformations and under many conditions there still result bodies of rockor integral material too large to be readily handled and requiringfurther breaking down.

It is a particular object of the invention to provide a portablesecondary blasing unit which can be hand carried and can be placed on alarge body of such material and which when detonated will causefragmentation of the body into pieces which are readily handled and willin effect cause the body to be reduced to small fragments.

Another object of the invention is to provide a sec ondary blasting unitwhich can be utilized with safety, yet which is effective to produce theresult desired.

Another object of the invention is to provide a sec ondary blasting unitso arranged as to utilize the capabilities of a shaped explosive chargeso as to concentrate the effect of an explosion onto a particular bodyto be fragmented and in a particular path.

Another object of the invention is to provide a sec ondary blasting unitwhich can easily and cheaply be manufactured and which is reliable inits operation.

Another object of the invention is to provide a secondary blasting unitso constructed as to be usable not only in the atmosphere under ordinarycircumstances, but also to be usable subaqueously when occasionsrequire.

Another object of the invention is in general to improve secondaryblasting units.

Other objects together with the foregoing are attained in the form ofthe invention described in the accompanying description and illustratedin the accompanying drawings, in which:

FIGURE 1 is a plan of one form of secondary blasting unit constructedpursuant to the invention;

FIGURE 2 is a bottom plan view of the structure shown in FIG. 1;

FIGURE 3 is a transverse vertical cross section, the plane of which isindicated by the line 3-3 of FIGURE 1; and

FIGURE 4 is an enlarged, fragmentary, side elevational view of theradial boss showing the arrangement of the exterior-opening detonatingcap cavity and, in outline, the interior opening recesses containing thetwo ends of the primer cord.

A practical embodiment of our secondary blasting unit, one which hasserved to illustrate and carry out the principles of the inventionincludes a casing 6. This is conveniently fabricated with asubstantially uniform wall. A suitable material is a plastic that can bereadily molded into an approximately or substantially dome shape. Thedome is planar in the upper central portion 7 and has curved Walls 8surrounding the central portion. The entire dome is preferablysymmetrical about a central axis 9 except for minor deviations. The dometerminates in a peripheral rim 11 and encloses a central chamber 12.

3,244,102 -Patented Apr. 5, 1966 Conveniently the rim 11 is extended inone area to afford a carrying handle 13.

Designed to fit on and cooperate with the dome casing in enclosing thecavity 12 is a cover 16. This is likewise symmetrical about the centralaxis 9 when in position and is coterminous with the rim 11. To securethe cover 16 on the casing both parts are formed with appropriate matingportions. Upstanding around the edge of the cover is a contoured rib 17substantially like an arrowhead in cross section. This is received in acorresponding groove 18 within the rim 11. When the cover 16 is forcedupon the casing, the parts snap together and are permanently retainedduring normal storage and transport. The cover also is provided near oron its rim with three feet 19 conveniently quite sharp.

The cover 16 is not fiat, but has a particular configuration in order totake advantage of the characteristics of a shaped charge of explosives.Preferably the cover 16 is of a shallow or relatively flat conicalconfiguration for the most part symmetrical about the axis 9. Also, thecover is contoured to define a semi-toroidal concavity 20 openingoutwardly and terminating on the conical portion of the cover so thatthe cone of action 21 of the toroidal portion, as illustrated by thelines 22 and 23, is symmetrical with the axis 9 and converges downwardlyaway from the chamber 12.

Within the chamber 12 a charge 25 of an explosive is situated. Disposedin juxtaposition to the explosive charge and arranged symmetrically inan annular channel 26 forming part of the casing 6 is a cord primer 27effective when ignited to ignite the charge 25. The cord primer 27 isreferred to as Primacord in the trade. It terminates in a pair of endseach received in one of a pair of interiorly opening recesses 31 and 32formed in a radial boss 33 projecting outwardly from the channel 26 andfrom the curved portion 8 of the dome 6. The ends of the Primacord aresubstantially parallel to each other and are firmly secured byfrictional fit within their individual recesses.

Particularly in accordance with the invention, the ends of the Primacord31 and 32 are not exposed exteriorly of the blasting unit, but ratherare protected from the outside by the closed ends of the recesses. Theboss 33 is additionally provided with an exterior opening cavity 34which does not communicate with the chamber 12 but does extend alongsideof and close to the recesses 31 and 32, leaving therebetween relativelythin, plastic walls 36 and 37. The thickness and resistance of the walls36 and 37 is such that a detonating cap disposed within the cavity 34and exploded is effective to shatter the frangible walls 36 and 37 andto ignite the Primacord which sets off the charge 25.

In the preferred manner of use of the device, it is placed fully chargedand provided with a detonating cap on the object to be fragmented. Thisis often a boulder or large rock and the legs or feet 19, beingrelatively sharp or pointed, engage into recesses or concavities in therock so that the blasting unit is firmly and easily put into position.The direction of the expected blast is arranged to correspond generallyto the direction of the central axis 9. By utilizing the handle 13 andotherwise orienting the casing of the unit, it can be positioned so thatthe blast direction is as desired. The placement can be in theatmosphere or under water since the entire charge and the Primacord arecompletely protected from the atmosphere and deleterious externalinfluences by the tightly engaged cover and casing.

Once the secondary blasting unit has been appropriately positioned, thedetonating cap is appropriately set off and the Primacord is ignitedthrough the so-fractured, intervening frangible walls 36 and 37. Theignited Primacord, being arranged in a nearly closed loop and actingvery quickly, in turn sets otf the charge 25 by almost simultaneousignition of a top, ring-like portion substantially above the concavity2t). This affords what we call ring ignition and is productive ofimproved detonation of the explosive charge and accentuates the efiectof the toroidal blast. The force of the explosion is directed not onlyby the curved walls 8. the planar wall 7 and the conical wall 16, butparticularly is directed and channeled by the configuration of thetoroidal portion 20 so that a concentrated, convergent blast is directeddownwardly along the central axis 9.

In practice it has been found that rocks or boulders of several cubicfeet in content can be shattered to crusher size by the use of asecondary blasting unit of the configuration and characteristicsdescribed herein.

What is claimed is:

1. A secondary blasting unit comprising:

(a) a casing of substantially dome shape terminating in a lower circularrim and being substantially concentric with a central axis;

(b) a radial boss on the upper portion of said casing,

said boss being formed with an exterior-opening cavity to receive adetonating cap, said boss also including a pair of interior-openingrecesses alongside said cavity and separated therefrom by frangiblewalls;

(c) a bottom cover mounted on and extending across said lower circularrim of said casing, said cover including a downwardly opening,semi-toroidal concavity concentric with said central axis;

(d) an explosive charge in said casing; and,

(e) a primer cord in said casing in contact with said charge, said cordbeing annularly disposed substantially concentric with said central axisand with a diameter substantially equal to the mean diameter of saidsemi-toroidal concavity, the ends of said primer cord terminating insaid recesses.

2. The device of claim 1 further characterized by at least two legsextending downwardly from said cover, said legs having a height notgreater than one-fifth the height of said casing.

3. The device of claim 1 wherein said casing is provided with a handleextending from said rim.

4. A secondary blasting unit comprising:

(a) a dome-shaped casting substantially concentric with 1 a central,vertical axis, said casting terminating in a substantially circularlower rim;

(b) a bottom cover substantially circular in outline mounted on saidlower rim and entirely enclosing the bottom of said casing, said coverhaving formed therein a downwardly opening semi-toroidal concavitysubstantially concentric with said central vertical axis;

(0) a radial boss on the upper portion of said casing,

said boss being formed with an exterior-opening cavity to receive adetonating cap, and a pair of interioropcning recesses alongside saidcavity and separated therefrom by frangible walls;

(d) an explosive charge in said casing;

(e) an annular channel on the upper portion of said casing substantiallyconcentric with said central axis, said channel being in communicationat its opposite ends with said pair of recesses and open at the bottomto said explosive charge; and,

(f) a primer cord formed into a loop within said annular channel, theends of said cord terminating in said pair of recesses and beingignitable by a detonating cap detonated, within said cavity, said capbeing capable of shattering said frangible walls separating said cavityfrom said pair of recesses.

5. A secondary blasting unit as in claim 4 in which said cover isprovided with legs and in which said casing is provided with a handle.

References Cited by the Examiner UNITED STATES PATENTS 2,513,233 6/1950Byers 10224 2,839,997 6/1958 Church et al 10224 2,984,307 5/1961 Barnes10224 2,988,994 6/1961 Fleischer et al. 10224 3,117,518 1/1964 Porter etal. 10224 3,119,178 1/1964 Owen et a1 102-24 FOREIGN PATENTS 1,092,56311/1954 France. 1,051,708 2/1959 Germany.

90,705 12/1957 Norway.

ENJAMIN A. BORCHELT, Primary Examiner.

1. A SECONDARY BLASTING UNIT COMPRISING: (A) A CASING OF SUBSTANTIALLYDOME SHAPE TERMINATING IN A LOWER CIRCULAR RIM AND BEING SUBSTANTIALLYCONCENTRIC WITH A CENTRAL AXIS; (B) A RADIAL BOSS ON THE UPPER PORTIONSAID CASING, SAIDBOSS BEING FORMED WITH AN EXTERIOR-OPENING CAVITY TORECEIVE A DETONATING CAP, SAID BOSS ALSO INCLUDING A PAIR OFINTERIOR-OPENING RECESSES ALONG SIDE SAID CAVITY AND SEPARATED THEREFROMBY FRANGIBLE WALLS; (C) A BOTTOM COVER MOUNTE ON SAID EXTEDNING ACROSSSAID LOWER CIRCULAR RIM OF SAID CASING, SAID COVER INCLUDING ADOWNWARDLY OPENING, SEMI-TOROIDAL CONCAVITY CONCENTRIC WITH SAID CENTRALAXIS; (D) AN EXPLOSIVE CHARGE IN SAID CASING; AND, (E) A PRIMER CORD INSAID CASING IN CONTACT WITH SAID CHARGE, SAID CORD BEING ANNULARLYDISPOSED SUBSTANTIALLY CONCENTRIC WITH SAID CENTRAL AXIS AND WITH ADIAMETER SUBSTANTIALLY EQUAL TO THE MEANS DIAMETER OF SAID SEMI-TOROIDALCONCAVITY, THE ENDS OF SAID PRIMER CORD TERMINATING IN SAID RECESSES.